HONOLULU -- Rural Hawaii residents still recovering from a tropical storm are keeping a nervous eye on a lava flow that may reach their community within a week.

Lava from Kilauea volcano is within less than nearly 2 kilometres of Kaohe Homesteads, authorities said. Lava could reach the community in five to seven days if it continues on its current path, geologists with the Hawaiian Volcano Observatory said.

It wasn't immediately clear how many homes could be affected.

The isolated, agricultural region is part of the Big Island's Puna district, where Tropical Storm Iselle toppled trees and knocked out power just last month.

Observatory scientists said the lava has been advancing about 244 metres per day since July 10. They've been closely monitoring the flow and on Thursday raised the alert level from "watch" to "warning."

However, the observatory said predicting a flow's exact path can be difficult because of subtle variations in topography, changes in lava volume and where and how lava enters or exits ground cracks.

Hawaii County Civil Defence Administrator Darryl Oliveira said the agency has not yet ordered an evacuation but will do so when it's clear the lava is at least five days from impacting homes.

Mayor Billy Kenoi is declaring an emergency, which will allow authorities to restrict access to roadways so Kaohe Homesteads residents can leave safely if an evacuation becomes necessary.

The county is asking all of Puna to be on alert because it's possible the lava could change direction and threaten other communities, he said.

The Kilauea volcano has been continuously erupting since 1983, but new vents -- or points where lava reaches the surface -- have opened periodically. Lava from the volcano normally doesn't approach homes, but it did wipe out neighbourhoods in 1990.